System and method of controlling a vehicle having yaw stability control

Abstract

The present invention involves a method of controlling a vehicle having a steer-by-wire system with enhanced yaw stability during a yaw motion disturbance. The method includes generating a steering angle signal of the steer-by-wire system. The steering angle signal is indicative of a steering angle. The method further includes generating an extra road wheel angle signal using a gain scheduled proportional-integral control strategy and an instant proportional-integral control strategy configured to attenuate after a predetermined time lapse from a time zero. The extra road wheel angle signal is indicative of an extra road wheel angle to compensate for the yaw motion disturbance defining the time zero. The method further includes generating a road wheel angle signal indicative of a road wheel angle and applying torque to the road wheels to move the road wheels consistent with the road wheel angle based on the road wheel angle signal.

What is claimed is:  
     
       1. A method of controlling a vehicle having a steer-by-wire system with enhanced yaw stability during a yaw motion disturbance, the method comprising: 
       sensing a steering wheel angle, speed, and yaw rate of the vehicle;  
       generating a steering angle signal of the steer-by-wire system, the steering angle signal being indicative of a steering angle based on steering wheel angle and steering ratio;  
       generating an extra road wheel angle signal implementing a gain schedule proportional-integral control strategy and an instant proportional-integral control strategy, the extral road wheel angle signal being indicative of an extra road wheel angle to compensate for the yaw motion disturbance defining a time zero;  
       generating a road wheel angle signal indicative of a road wheel angle, the road wheel angle being based on the extra road wheel angle and the steering wheel angle before a predetermined time lapse, the road wheel angle being based on the steering wheel angle after the predetermined time lapse relative to a time zero; and  
       applying torque to the road wheels to move the road wheels based on the road wheel angle.  
     
     
       2. The method of  claim 1  wherein the Gain scheduled proportional-integrated control strategy includes:            K   p     =       P   1         P   2     +       k   p          V   spd             ,                  and                   K   i       =       I   1         I   2     +       k   i          V   spd             ,                   
       where K p  is indicative of proportional gain; K i  is indicative of integral gain; V spd  is indicative of Vehicle speed; P 1 , P 2 , k p  are constants for gain-scheduled proportional control; and I 1 , I 2 , k i  are constants for gain-scheduled integral control. 
     
     
       3. The method of  claim 2  wherein the instant Proportional and Integral control strategy includes:              K   ip          (   z   )       =       k   ip                           a   p0          z   2       +       a   p1          z   1       +     a   p2           z   2     +       b   p1          z   1       +     b   p0             ,              and                 K   ii          (   z   )       =       k   ii                           a   i0          z   2       +       a   i1          z   1       +     a   i2           z   2     +       b   i1          z   1       +     b   i0             ,                   
       where z k  is indicative of time shift operator which shifts the time by k units; k ip  is indicative of gain for P attenuator; k ii  is indicative of gain for I attenuator; a pk , b pk  are indicative of constants for P attenuator; and a ik , b ik  are indicative of constants for I attenuator. 
     
     
       4. The method of  claim 1  wherein the estimated side slip includes a saturator for control output including:        control   =     {             (           K   ip          (   z   )            K   p       +         K   ii          (   z   )            K   i         )     *     Yaw   error               if                   abs        (   contol   )         <     control   thd                 control   thd             if                 control     >=                control   thd                 -     control   thd               if                 control     <=     -     control   thd                                 
       where Yaw error  is indicative of a difference between the measured yaw rate and the desired yaw rate; and Control thd  is indicative of a control threshold, the control threshold being determined by:          control   thd     =       control   max     *   min        {       1       control   Vpd     +       k   vpd          V   spd           ,                1       control   lat     +       k   lat        Lat         ,                1       control   ss     +       k   ss        sideslip           }                       
       where Control max  is indicative of maximal control output; Lat is indicative of lateral acceleration; Sideslip is indicative of sideslip angle; Control vpd , k vpd  is indicative of constants of saturator with respect to vehicle speed; Control lat , k lat  is indicative of constants of saturator with respect to vehicle's lateral acceleration; and Control ss , k ss  is indicative of constants of saturator with respect to vehicle's sideslip angle. 
     
     
       5. The method of  claim 1  further comprising comparing the yaw error with the error thresholds. 
     
     
       6. The method of  claim 1  wherein the steer-by-wire system includes a sampling period of about 1 microsecond. 
     
     
       7. The method of  claim 1  wherein the predetermined time lapse is about 0.5 second. 
     
     
       8. The method of  claim 1  further comprising generating the road wheel command reference signal indicative of a road wheel command reference, the road wheel command reference being based on a predetermined steering ratio and the steering wheel angle. 
     
     
       9. The method of  claim 1  further comprising: 
       calculating the extra road wheel angle, if the yaw error is determined to be greater than an error threshold; and  
       calculating a road wheel angle based on the extra road wheel angle.  
     
     
       10. The method of  claim 4  further comprising: 
       calculating the estimated side slip angle based on the road wheel angle, speed and the yaw rate of the vehicle.  
     
     
       11. The method of  claim 1  further comprising: 
       sensing lateral acceleration of the vehicle;  
       generating a desired yaw rate signal indicative of a desired yaw rate, the desired yaw rate being based on the steering wheel angle and the vehicle speed;  
       generating a yaw error signal indicative of a yaw error, the yaw error being based on the desired yaw rate and the measured yaw rate;  
       determining the desired yaw rate based on the steering wheel angle and the vehicle speed; and  
       determining the yaw error based on the desired yaw rate and the measured yaw rate.  
     
     
       12. The method of  claim 11  further comprising determining whether an estimated side slip is greater than a side slip threshold. 
     
     
       13. The method of  claim 12  further comprising: 
       generating an estimated side slip signal indicative of the estimated side slip of the vehicle based on the road wheel angle, speed, and the yaw rate of the vehicle; and  
       generating a steering wheel angle signal indicative of the steering wheel angle, a lateral acceleration signal indicative of lateral acceleration, a vehicle speed signal indicative of vehicle speed, a yaw rate signal indicative of yaw rate, and an estimated side slip signal indicative of the estimated side slip.  
     
     
       14. The method of  claim 1  wherein the compensating steering angle has a maximum angle based on the speed of the vehicle. 
     
     
       15. The method of  claim 14  wherein the maximum steering angle is about +/−3° if the vehicle speed is determined to be less than 20 miles per hour and the maximum steering angle is about +/−1°, if the vehicle speed is determined to be greater than 60 miles per hour. 
     
     
       16. The method of  claim 1  wherein generating the desired yaw rate signal includes: 
       receiving the steering wheel angle and the vehicle speed; and  
       prefiltering the steering wheel angle and vehicle speed.  
     
     
       17. The method of  claim 16  wherein the step of filtering includes:          r   des     =       VhSpd   *   Steeringratio   *   SWA       L   +     K   *       VhSpd                2                           
       r des  is indicative of desired yaw rate; L is indicative of wheelbase of the vehicle; K is indicative of understeer coefficient; Vh Spd is indicative of vehicle speed; and SWA is indicative of steering wheel angle. 
     
     
       18. The method of  claim 1  wherein generating the compensating steering angle signal and generating the extra road wheel angle signal are performed, if a yaw error is determined to be greater than an error threshold. 
     
     
       19. The method of  claim 18  wherein the error threshold is 1 degree per second. 
     
     
       20. The method of  claim 1  wherein the error threshold is about 0.1 to 2.0 degrees per second. 
     
     
       21. A method of controlling a vehicle having a steer-by-wire system with enhanced yaw stability during a yaw motion disturbance, the method comprising: 
       sensing a steering wheel angle, lateral acceleration, speed, and a yaw rate of the vehicle;  
       generating a desired yaw rate signal indicative of a desired yaw rate, the desired yaw rate being based on the steering wheel angle and the vehicle speed;  
       generating a yaw error signal indicative of a yaw error, the yaw error being based on the desired yaw rate and the measured yaw rate;  
       generating a compensating, steering angle signal of the steer-by-wire system implementing a gain scheduled proportional-integral control strategy and an instant proportional-integral control strategy the compensating steering angle signal being indicative of a compensating steering angle, if the yaw error is determined to be greater than an error threshold;  
       generating an extra road wheel angle signal indicative of an extra road wheel angle to compensate for the yaw motion disturbance defining a time zero, if the yaw error is determined to be greater than an error threshold;  
       generating a road wheel angle signal indicative of a road wheel angle, the road wheel angle being based on the extra road wheel angle and a steering wheel angle before a predetermined time lapse, the road wheel angle being based on the steering wheel angle after the predetermined time lapse relative to the time zero; and  
       applying torque to the road wheels to move the road wheels consistent with the road wheel angle.  
     
     
       22. The method of  claim 21  wherein the Gain scheduled proportional-integrated control strategy includes:            K   p     =       P   1         P   2     +       k   p          V   spd             ,              and               K   i     =       I   1         I   2     +       k   i          V   spd             ,                   
       where K p  is indicative of proportional gain; K i  is indicative of integral gain; V spd  is indicative of Vehicle speed; P 1 , P 2 , k p  are constants for gain-scheduled proportional control; and I 1 , I 2 , k i  are constants for gain-scheduled integral control. 
     
     
       23. The method of  claim 22  wherein the instant Proportional-integral control strategy includes:              K   ip          (   z   )       =       k   ip                           a   p0          z   2       +       a   p1          z   1       +     a   p2           z   2     +       b   p1          z   1       +     b   p0             ,              and                 K   ii          (   z   )       =       k   ii                           a   i0          z   2       +       a   i1          z   1       +     a   i2           z   2     +       b   i1          z   1          b   i0               ,                   
       where z k  is indicative of time shift operator which shifts the time by k units; k ip  is indicative of gain for P attenuator; k ii  is indicative of gain for I attenuator; a pk , b pk  are indicative of constants for P attenuator; and a ik , b ik  are indicative of constants for I attenuator. 
     
     
       24. The method of  claim 23  wherein the estimated side slip includes a saturator for control output including:        control   =     {             (           K   ip          (   z   )            K   p       +         K   ii          (   z   )            K   i         )     *     Yaw   Error               if                   abs        (   control   )         <     control   thd                 control   thd             if                 control     >=     control   thd                 -     control   thd               if                 control     <=     -     control   thd                                 
       where Yaw error  is indicative of a difference between the measured yaw rate and the desired yaw rate; and Control thd  is indicative of a control threshold, the control threshold being determined by:          control   thd     =       control   max     *   min        {       1       control   Vpd     +       k   vpd          V   spd           ,                1       control   lat     +       k   lat        Lat         ,                1       control   ss     +       k   ss        sideslip           }                       
       where Control max  is indicative of maximal control output; Lat is indicative of lateral acceleration; Sideslip is indicative of sideslip angle; Control vpd , k vpd  is indicative of constants of saturator with respect to vehicle speed; Control lat , k lat  is indicative of constants of saturator with respect to vehicle's lateral acceleration; and Control ss , k ss  is indicative of constants of saturator with respect to vehicle's sideslip angle. 
     
     
       25. The method of  claim 1  further comprising comparing the yaw error with the error thresholds. 
     
     
       26. The method of  claim 1  wherein the error threshold is 1 degree per second. 
     
     
       27. The method of  claim 1  wherein the predetermined time lapse is about 0.5 second. 
     
     
       28. The method of  claim 1  further comprising generating the road wheel command reference signal indicative of a road wheel command reference, the road wheel command reference being based on a predetermined steering ratio and the steering wheel angle. 
     
     
       29. The method of  claim 1  further comprising: 
       calculating the extra road wheel angle, if the yaw error is determined to be greater than an error threshold; and  
       calculating a road wheel angle based on the extra road wheel angle.  
     
     
       30. The method of  claim 4  further comprising: 
       calculating the estimated side slip angle based on the road wheel angle speed and the yaw rate of the vehicle.  
     
     
       31. The method of  claim 21  further comprising: 
       determining the desired yaw rate based on the steering wheel angle and the vehicle speed; and  
       determining the yaw error based on the desired yaw rate and the measured yaw rate.  
     
     
       32. The method of  claim 31  further comprising determining whether an estimated side slip is greater than a side slip threshold. 
     
     
       33. The method of  claim 32  further comprising: 
       generating an estimated side slip signal indicative of the estimated side slip of the vehicle based on the road wheel angle, speed, and the yaw rate of the vehicle; and  
       generating a steering wheel angle signal indicative of the steering wheel angle, a lateral acceleration signal indicative of lateral acceleration, a vehicle speed signal indicative of vehicle speed, a yaw rate signal indicative of yaw rate, and an estimated side slip signal indicative of the estimated side slip.  
     
     
       34. The method of  claim 1  wherein the compensating steering angle has a maximum angle based on the speed of the vehicle. 
     
     
       35. The method of  claim 14  wherein the maximum compensating steering angle is about +/−3° if the vehicle speed is determined to be less than 20 miles per hour and the maximum compensating steering angle is about +/−1° if the vehicle speed is determined to be greater than 60 miles per hour. 
     
     
       36. The method of  claim 1  wherein generating the desired yaw rate signal includes: 
       receiving the steering wheel angle and the vehicle speed; and  
       prefiltering the steering wheel angle and vehicle speed.  
     
     
       37. The method of  claim 16  wherein the step of filtering includes:          r   des     =       VhSpd   *   Steeringratio   *   SWA       L   +     K   *       VhSpd                2                           
       r des  is indicative of desired yaw rate; L is indicative of wheelbase of the vehicle; K is indicative of understeer coefficient; VhSpd is indicative of vehicle speed; and SWA is indicative of steering wheel angle. 
     
     
       38. A system for controlling a vehicle having a steer-by-wire system with enhanced yaw stability during a yaw motion disturbance, the system comprising: 
       a driver interface system for sensing a steering wheel angle of the vehicle;  
       an electronic control unit configured to generate a road wheel angle signal to compensate for the yaw motion disturbance, the road wheel angle being based on an extra road wheel angle and a steering wheel angle before a predetermined time lapse, the road wheel angle being based on the steering wheel angle after the predetermined time lapse relative to the time zero; and  
       a road wheel actuating system for sensing lateral acceleration, speed, and measured yaw rate of the vehicle and for applying torque to the road wheels to move the road wheels consistent with the road wheel angle based on the road wheel angle signal and the predetermined steering ratio.  
     
     
       39. The system of  claim 38  wherein the electronic control unit is configured to generate a desired yaw rate signal based on the steering wheel angle and the vehicle speed and generate a yaw error signal based on the desired yaw rate and the measured yaw rate. 
     
     
       40. The system of  claim 39  wherein the electronic control unit is configured to generate a compensating steering angle signal of the system implementing a gain scheduled proportional-integral control strategy and an instant proportional-integral control strategy. 
     
     
       41. The system of  claim 40  wherein the electronic control unit is configured to generate the compensating steering angle signal, if the yaw error is determined to be greater than an error threshold.